This invention relates to luboil viscosity index improvers (VII) having improved viscoelastic properties. In another aspect, the invention relates to mineral lubricating oil compositions containing such VII additives.
A variety of polymeric materials are available to improve the viscosity index of lubricating oils intended for use in internal combustion engines. Such materials include hydrogenated styrene/isoprene diblock copolymers, olefin copolymers, and hydrogenated star (radial) copolymers having a divinylbenzene-derived nucleus and polyolefin arms. Continuing development of engines places increasing demands on the performance characteristics of lubricating oils, leading to continual efforts to achieve property benefits additional to the basic VII effect. One such property is the viscoelastic behavior, and applicants have now discovered that this property can be beneficially modified by the introduction of carboxyl groups onto the polymeric chains.